The present invention relates to a compacting facility for bulk goods having a roller press and a screw conveyor positioned before it, over which a feeding hopper is positioned as bulk good feeder.
Crude products, which are supplied as a powder or grain or a mixture thereof, are frequently not suitable for immediate further processing, e.g. into tablets in the pharmaceutical industry, because they have too high a proportion of air and/or are not sufficiently pourable. Compacting the crude products before the further processing and subsequently granulating them is known from the patent literature (German Patent 34 31 865 C2), but above all from practice. For compacting, for example, a roller press having a screw conveyor positioned before it is used. Using the screw conveyor, the crude product is fed into the roller gap from the feeding hopper under a certain pressure. Since the roller press is sealed on both sides and the screw conveyor is connected tightly to the roller gap, the air pressed out of the crude product during compacting must travel through the material flow in the screw housing against its direction of conveyance. The air may then only escape via the material column located in the feeding hopper, which, however, offers a certain resistance to the air as a function of its height and density. However, a part of the air also passes through the roller gap “explosively”, due to which the roller press is stressed and runs noisily.
In compacting it is important that the flakes which arise during compacting are as homogeneous as possible, because this property directly affects the final product. If the crude product in the feeding hopper is not uniformly distributed in regard to the grain size or in regard to other properties, inhomogeneous flake qualities occur. This is particularly the case if a portion of the compacted material which does not have the desired grain size after granulation is recirculated to the feeding hopper. The direct recirculation of this compacted crude product is not unproblematic because the bulk densities of this compacted crude product and of the untreated crude product are very different. An untreated product, which has a bulk density of 200 g/l, may have a bulk density of 800 g/l as the recirculated material after compacting. This is made more difficult because the mass flow of the recirculated product varies greatly. For soft flakes, the proportion of the mass flow of the recirculated product fed to the roller press is large, which has a favorable effect on homogeneous flake quality, but this in turn has the consequence that the mass flow of the recirculated material falls. Therefore, stabilization of the flake quality only occurs slowly in the process. For this reason, until now the mass flow of the recirculated material was subjected to an additional mixing procedure with the crude product before compacting.
Furthermore, a compacting facility for bulk goods is known (German Patent Application 38 06 398 A1), in which a feeding hopper having two shafts is positioned over a roller press, from which the roller gap may be fed in parallel with various types of bulk goods. The proportions of the various types of bulk goods which are fed to the roller gap from the various shafts may be adjusted by a metering element. Separate premixing of the bulk goods before the roller gap is not provided. The bulk goods come out of the roller gap pulverized and partially agglomerated, i.e., compressed into flakes. As a rule, the flakes are ground in a ball mill to the final fineness and supplied to a sifter, whose coarse output is recirculated as a fine product into the shaft having the fine product feed. The deaeration of the bulk goods occurs via the material column in the shaft for the coarse bulk good.